The present invention relates to strain relief devices in general and more specifically to an expandable strain relief for use with flexible, cable-like members.
Strain relief devices are well-known in the art and have been used for decades to prevent strain placed on cable-like members from being transferred to a connection made at the end of the cable. For example, strain relief devices for electrical cables typically transfer cable strain to a mounting bracket or chassis associated with the device, thereby greatly increasing the reliability of the electrical connection at the end of the cable. Strain relief devices come in a wide range of types and styles and are used in conjunction with nearly all types of electrically powered devices and appliances in industrial, commercial, and home applications.
While strain relief devices of the type described above are typically used to absorb and/or transfer strain applied to electrical cables and wires, the recent advent of fiber optic cables for transferring information and data between two or more devices has created a need to provide some sort of strain relief device for fiber optic cables. Unfortunately, however, the physical characteristics and construction of fiber optic cables precludes the use of strain relief devices designed for use with electrical cables and wires. For example, most strain relief devices for electrical cables and wires function by tightly gripping or crimping the cable or wire. This does not pose a problem in electrical applications since most electrical cables and wires are sufficiently mechanically robust to resist such crimping forces without affecting their ability to transmit the electrical signal. However, the same cannot be said for fiber optic cables.
A typical fiber optic cable assembly comprises one or more individual fiber optic strands or xe2x80x9cfibersxe2x80x9d which conduct light by total internal reflection. The individual strands or fibers are typically fabricated from a transparent material, such as glass, although other materials can be used. The glass fiber may be coated or xe2x80x9cdopedxe2x80x9d with another material having a refractive index that is less than that of the glass fiber. Such an arrangement allows light entering the end of the glass fiber to be conducted or guided along the fiber by means of total internal reflection. The glass fiber that actually transmits or conducts the light is commonly referred to as the core, while the surrounding material or dopant is typically referred to as the cladding. As mentioned above, one or more individual strands or fibers are typically bundled together to form the fiber optic cable. The fiber optic cable may then be covered with a cover or sheath to protect the fibers comprising the optic cable. The sheath may comprise any of a wide range of flexible plastic or rubber-like materials, depending on the particular application.
Regardless of the particular construction of the fiber optic cable, most fiber optic cables cannot tolerate excessive gripping or crimping forces, such as those typically applied by known strain relief devices. More specifically, such gripping or crimping forces may cause extreme bending of the optic fibers, which decreases or prevents them from conducting light across the bend. In extreme cases, the gripping or crimping forces may even fracture one or more of the individual optic fibers comprising the optic fiber cable.
Another characteristic of optic fiber cables that exacerbates the strain relief problem is that it is difficult to cut and/or splice the optic fiber in the field in order to shorten or lengthen the cable for a particular installation. Accordingly, most users of fiber optic cables obtain cables of at least the minimum lengths required. The extra lengths must then be accommodated somewhere in the installation. Since most fiber optic cables are supplied in a limited number of predetermined lengths, many users are faced with the task of accommodating a significant amount of extra cable length. Besides creating installation problems, such additional lengths can increase the likelihood that a user or other person will accidently become entangled in the extra cabling, increasing the chances that undue stress will be applied to the cable.
One type of strain relief system that has been developed for such fiber optic cables that provides some degree of strain relief as well as extra cable take-up comprises a foam-lined clamp assembly. The fiber optic cable may be secured within the foam-lined clamp, which supports the cable. Several such clamp assemblies can be used to route the fiber optic cable and provide the take-up required to store any extra cable length. Unfortunately, however, such foam-lined clamps are not without their problems. For example, such foam-lined clamp assemblies do not constrain the bend radius of the fiber cable. Consequently, excessive signal loss may occur if the cable is looped or wrapped too tightly around the strain relief (i.e., if the bend radius is too small). Another problem is that while the foam-lining on the clamp assembly prevents the clamp from exerting excessive force on the cable, it also limits the strain relief effectiveness, since the cable can easily slip within the foam-lined clamp.
Consequently, a need remains for a strain relief device that is suitable for use with fiber optic cable assemblies. Such a strain relief device should provide effective and robust strain relief to the cable, but without applying excessive crimping forces to the cable, which can degrade cable performance and may even damage the cable. Additional advantages could be realized if the strain relief device were also capable of providing the take-up necessary to absorb extra cable length.
A strain relief according to one preferred embodiment of the present invention may comprise a spool-like member defining at least one radial slot therein that extends along a portion of the length of the spool-like member. The radial slot divides the spool-like member into a first hemi-spool portion and a second hemi-spool portion. The radial slot also defines a bridge section that connects the first and second hemi-spool portions. The bridge section is severable to allow the second hemi-spool portion to be separated from the first hemi-spool portion.
Also disclosed is a method for relieving strain from a flexible, cable-like member that comprises the steps of: Providing a spool-like member having a radial slot therein that extends along a portion of the length of the spool-like member, the radial slot dividing the spool-like member into first and second hemi-spool sections, the radial slot also defining a bridge section connecting the first and second hemi-spool sections; and wrapping a portion of the flexible, cable-like member at least partially around the spool-like member.